Method for glass making using an oxy-fuel fired distribution channel

Abstract: A method of making glass articles, wherein glass flows from a furnace, through a distribution channel, and then to forming means, the method comprising forming at least one oxy/fuel flame at the sides of the distribution channel, the flame having a hottest point within about five inches of the base of the flame so as to produce a large thermal gradient between the sides of the distribution channel and the center of the distribution channel. A novel distribution channel and a method and apparatus for producing an oxy/fuel flame having a hottest point within about five inches of the base of the flame are also disclosed.

Description: The present invention relates to a method of glass making using an oxy/fuel fired distribution channel. History of the Prior Art In the production of glass, a distribution channel has two main purposes. First, the distribution channel delivers molten glass from the furnace to the forming means. Second, the distribution channel modifies the temperature of the molten glass. Usually, the temperature of the molten glass must be lowered. Modifying the temperature of the molten glass brings the glass to a viscosity required for forming. Viscosity requirements vary widely depending on the glass and forming means used. Uniformity of temperature for all glass entering the forming means is the measure of excellence. Uniformity of gob weight or product dimensions are dependent upon uniform temperatures in the gob. However, modifying the temperature of molten glass in a distribution channel is difficult due to temperature differences existing in the glass. The glass at the sides of the distribution channel is cooler than the glass in the center of the distribution channel. This is because the glass at the sides of the channel transfers heat through the walls of the channel, while the glass in the center of the channel is insulated from heat loss by the surrounding glass. Thus, it is usually necessary to heat the glass at the sides of the distribution channel so as to raise its temperature to that of the glass in the center of the channel. Conversely, the glass in the center of the distribution channel is usually simultaneously cooled so as to lower its temperature to that of the glass at the sides of the channel. The temperature of the glass at the sides of the distribution channel is commonly raised with burners. Recently, a few glassmakers have tried oxy/fuel burners in place of air/fuel burners. Attention is directed to EP-A-167447 and EP-A-216698, both of which describes the use of any oxy/fuel flame to heat molten glass flowing in a forehearth or distribution channel. Compared with air/fuel burners, oxy/fuel burners provide three times the available heat from the same fuel input and a significant reduction in NOx. One major problem has historically plagued the practice of heating the glass at the sides of a distribution channel with burners. The heat produced by the burners travels to the center of the channel. This heats the glass in the center of the channel, which should be cooled. To deal with this problem, wind cooling of the center of the distribution channel and "wings" substantially separating the center and sides of the channel have been utilized. However, energy from the burners still makes its way to the center of the channel, where the heating flames and cooling wind compete, making temperature uniformity difficult to achieve. Therefore, a need exists for a method of making glass comprising an improved method of modifying the temperature of the molten glass in a distribution channel. SUMMARY OF THE INVENTION According to the present invention there is provided a method of producing glass articles, wherein molten glass flows from a furnace, through a distribution channel, and then to forming means, said method including forming, by means of an oxy/fuel burner, at least one oxy/fuel flame directed from the sides of said distribution channel towards the center thereof, said flame having a hottest point within 127mm (five inches) of the face or outermost part of said burner (hereinafter referred to as the "base" of the flame) so as to produce a large thermal gradient between the sides of said distribution channel and the center of said distribution channel. The present invention allows glass at the sides of a distribution channel to be heated with burners, while greatly reducing any secondary heating affect on the glass in the center of the distribution channel. Also, use of any oxy/fuel flame having a hottest point within 127mm (five inches) of the base of the flame preferably provides a low level of products of combustion. The burner preferably provides between about 14 l/hr (0.5 SCFH) and 425 l/hr (15 SCFH) of fuel, more preferably between about 198 l/hr (7 SCFH) and 425l/hr (15 SCFH) of fuel. The present method of making glass articles may be used with other known methods of modifying the temperature of glass in a distribution channel. These known methods may include, for example, cooling the center of the distribution channel with a longitudinal flow of air, and/or separating the sides of the distribution channel from the center of the distribution channel by placing wings in the crown of the channel which project downward towards the surface of the glass flowing through the channel. The wings may project to any desired height, but preferably project to just above or just below the surface of the glass flowing through the distribution channel. Further advantageous aspects and developments of the invention will be apparent from the claims. BRIEF DESCRIPTION OF THE FIGURES Fig. 1 is a cross-sectional view and an end-view of part of an oxy/fuel burner for use in the method of the present invention. Fig. 1 shows the fuel tube and the oxygen tube, as well as the most preferred embodiment of the turbulence means. Fig. 2 is a cross-sectional view of an oxy/fuel burner for use in the method of the present invention. Fig. 3 is a cross-sectional illustration of a distribution channel for use in the method of the present invention. Fig. 4 is a cross-sectional view of an oxy/fuel burner for use in the method of the present invention having the fuel orifice behind the oxygen orifice. Fig. 5 is a cross-sectional view of an oxy/fuel burner for use in the method of the present invention having the fuel orifice in front of the oxygen orifice. Fig. 6 is an end-view of one embodiment of the fuel orifice and oxygen orifice of an oxy/fuel burner for use in the method of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is based on the discovery that use of one or more short oxy/fuel flames to heat the sides of a glass distribution channel significantly reduces the amount of heat energy which travels to the center of the distribution channel and which then causes deleterious heating of the glass in the center of the channel. Oxy/fuel firing provides superior characteristics over regular air/fuel firing. Oxy/fuel firing provides a significant reduction in NOx. Overall, oxy/fuel firing provides a 90% reduction in the volume, or mass, of exhaust gases, lowering turbulence and surface glass losses. Most important to the problems of glass distribution channels, oxy/fuel firing provides about three times the available heat from the same fuel input. Furthermore, the heat is very concentrated. Most of the heat from an oxy/fuel flame appears to be reflected from the cover block down to the molten glass. However, there is still horizontal heat transfer. The longer the flame, the more of the heat energy produced finds it way to the center of the channel. In the present method of producing glass articles, the hottest point of the flame produced to heat the sides of the distribution channel is within 127mm (five inches) of the base of the flame. Preferably, the hottest point of the flame is within 76mm (three inches) of the base of the flame. As stated above, the "base" of the flame is defined herein as the face or outermost part of the burner used to produce the flame. To carry out the present method of making glass articles, the present invention uses a novel distribution channel which comprises at least one oxy/fuel burner situated in the sides of the distribution channel, the at least one oxy/fuel burner capable of producing a flame having a hottest point within 127mm (five inches) of the base of the flame so as to produce a large thermal gradient between the sides of the distribution channel and the center of the distribution channel. The burners may be situated in the sides of the distribution channel via methods well known to those skilled-in-the-art. The burners may be placed within insulated burner blocks and situated at spaced intervals within the sides of the cover block. The burner block may have a flame tunnel to direct the oxy/fuel flame. When firing from the sides of a distribution channel, the short length of these flames combined with the efficient and concentrated oxy/fuel combustion provides for a significantly improved thermal gradient between the sides of the distribution channel and the center of the distribution channel. As used herein, "fuel" means any gaseous fuel suitable for glassmaking. Due to the efficiency of oxy/fuel firing, this low volume of fuel still produces significant heating. Despite the fact that the heat is brought closer to the burner, the present invention may be utilized without complicated and expensive cooling mechanisms to protect the burner. Furthermore, the wear and tear on other elements of the distribution channel caused by combustion products and turbulence is reduced. Fig. 3 is a cross-section illustration of the cooling zone of a distribution channel used in the method of the present invention. The distribution channel is about 2.74m (nine feet) long and is operated under pressure. The distribution channels sits in steel support 20. Molten glass 24 flows through a glass channel defined by support blocks 21, channel block insulation 22 and glass channel block 23. Covering the channel are cover block insulation 25 and cover block 26. Cover block 26 extends towards the molten glass 24, forming two wings 27. The center 28 of the channel is substantially separated from the sides 29 of the channel by wings 27. Cooling wind is blown longitudinally through the center 28 of the channel (i.e. - perpendicular to the plane of the page) by a cooling fan or other mechanism (not shown). Cooling wind is vented out exhaust stack 35. Insulated burner blocks 30 are situated at the sides of the distribution channel within cover block 26. Oxy/fuel burners 31 are situated within the burner blocks. The oxy/fuel burners 31 provide between about 14 l/hr (0.5 SCFH) and 4.25 l/hr (15 SCFH) of methane fuel. Flames 33 exit out of burner orifices 32. The flames' hottest points are within about 127mm (five inches) of the burner orifices 32. The flames travel through flame tunnels 34 which are formed within the burner blocks 30. The oxy/fuel burners 31 in the sides of the distribution channel are situated at 152mm (six inch) intervals along the sides of the distribution channel. Thirteen oxy/fuel burners 31 are placed on each side of the distribution channel. The present invention uses an oxy/fuel burner and related method for producing an oxy/fuel flame which has its hottest point within about 127mm (5 inches) of the base of the flame. One embodiment of the oxy/fuel burner comprises fuel means for projecting a stream of fuel from a fuel orifice at a volume of between about 198 l/hr (7 SCFH) and 425 l/hr (15 SCFH) of fuel, and oxygen means for projecting an annular stream of oxygen around the stream of fuel from an annular oxygen orifice surrounding the fuel orifice at an oxygen velocity to gas velocity ratio between about 1:1 and 3:1. Projecting the stream of oxygen around the stream of fuel causes significant mixing and a shorter burn time. By increasing the turbulence of either the oxygen stream, the fuel stream or both, mixing is significantly increased. This allows for the desired flame characteristics at a lower operable fuel flow. Thus, a preferred embodiment of the present oxy/fuel burner comprises fuel means for projecting a stream of fuel from a fuel orifice at a volume of between about 14 l/hr (0.5 SCFH) and 425 l/hr (15 SCFH) of fuel, oxygen means for projecting an annular stream of oxygen around the stream of fuel from an annular oxygen orifice surrounding the fuel orifice at an oxygen velocity to gas velocity ratio between about 1:1 and 3:1, and turbulence means for increasing turbulence in at least one of the streams. The oxygen velocity to gas velocity ratio of the present oxy/fuel burner and related method is preferably about 1.5:1. The specific velocities of the oxygen and fuel are dependent on a number of factors, including the oxygen and fuel supply pressures, the specific volume flow of the fuel, and the cross-sectional area of the fuel and oxygen orifices. Under most distribution channel conditions, it is preferred that the stream of fuel be projected from the fuel orifice at a velocity below about 152m/sec (500 ft./sec), and most preferably at a velocity below about 76m/sec (250 ft./sec). For a given pressure and flow rate, the velocities of the fuel stream and oxygen stream are dependent on the cross-sectional area of the fuel and oxygen orifices. The fuel orifices preferably has a cross-sectional area between about 1.026mm 2 (0.00159 square inches) and 4.103mm 2 (0.00636 square inches), and most preferably has a cross-sectional area of about 2.45mm 2 (0.0038 square inches). At 113 l/hr (4 SCFH) of fuel, the lower limit (1.026mm 2 ) (0.00159 square inches) will produce a fuel velocity of about 30m/sec (100 ft./sec), and the upper limit (4.103mm 2 ) (0.00636 square inches) will produce a fuel velocity of about 7.6m/sec (25 ft./sec). At 425 l/hr (15 SCFH) of fuel, the lower limit will produce a fuel velocity of about 114m/sec (375 ft./sec), and the upper limit will produce a fuel velocity of about 29m/sec (94 ft./sec). The fuel orifice may be placed in front of or behind the oxygen orifice, but is preferably flush with the oxygen orifice. In a preferred embodiment, the fuel means includes a fuel tube for receiving fuel at an inlet end and expelling fuel at an outlet end, and the oxygen means includes an oxygen tube for receiving oxygen at an inlet end and expelling oxygen at an outlet end, the oxygen tube surrounding the fuel tube. The oxygen tube and fuel tube may be multiple widths, having a larger width for receiving oxygen or fuel and narrowing, either suddenly or gradually, to a smaller width to provide the desired oxygen or fuel velocity at a given pressure. The oxygen and fuel tubes may be made from any suitable material, but are preferably made of a material selected from the group consisting of refractory metal and ceramic. In the most preferred scenario, the fuel tube is refractory metal, as metal is a better conductor of heat and resists fuel cracking, and the oxygen tube is ceramic, as ceramic resists oxidation. The fuel tube is preferably any thickness under about 1mm. The oxygen tube is preferably between about 0.4mm and 1.5mm thick and most preferably as thin as possible. The present oxy/fuel burner may replace air/fuel burners or other oxy/fuel burners currently in distribution channels. The fuel tube and oxygen tube may be held in position via apparatus well known to those skilled-in-the-art. Increasing turbulence in the oxygen stream and/or the fuel stream is critical to the preferred embodiment of the method of the present invention. The turbulence means of the present oxy/fuel burner may include known apparatus, such as, for example, rifling in the oxygen tube, a flared end to the fuel tube with the oxygen tube rearward, a quartered exit to the oxygen tube, rotated crosshairs in the end of the fuel tube, and a partially turned-in end to the oxygen tube. A preferred, novel turbulence means comprises at least one spiral wire fixed between the oxygen tube and the fuel tube so as to produce angular momentum in the oxygen stream. The spiral wires are preferably made of refractory metal. The spiral wire or wires may be tack welded to the outer diameter of the fuel tube or to the inner diameter of the oxygen tube, or may simply be held in place by the pressure of the wires against the two tubes. Use of a spiral wire is simple and may be used in conjunction with tubes of very small diameter without great difficulty. Furthermore, the oxygen stream, rather than the fuel stream, is used to increase the turbulence. As oxygen has a greater atomic weight than most of the fuels used in burners, it will cause a greater increase in turbulence than the fuel for a given annular momentum. A cross-sectional view of one embodiment of an oxy/fuel burner for use in the method of the present invention which was assembled for tests is illustrated in Fig. 2. Fuel inlet 10 can accept a fuel pipe carrying the applicable gaseous fuel. Oxygen inlet 11 can accept an oxygen pipe carrying gaseous oxygen. Fuel inlet 10 screws into the back of hollow brass body 12. Oxygen inlet 11 screws into the side of hollow brass body 12. Fuel tube 13 is inserted through the center of hollow brass body 12 and fuel inlet 10 and screws into panel 14 of fuel inlet 10. Oxygen tube 15 encircles fuel tube 13, and the back end of oxygen tube 15 is seated around the front nose of hollow brass body 12. The fuel tube 13 and the oxygen tube 15 are made of Inconel 600. The fuel tube has an inner diameter of about 1.78mm (0.070 inches) and an outer diameter of about 3.188mm (0.1255 inches). The oxygen tube has an inner diameter of about 4.762mm (0.1875 inches) and an outer diameter of about 6.261mm (0.2465 inches). Fuel fed through fuel inlet 10 travels to fuel tube 13 and then out fuel orifice 17. Oxygen fed through oxygen inlet 11 travels to the center of hollow brass body 12, surrounds fuel tube 13, and travels to oxygen tube 15 and out oxygen orifice 18. Spiral wire 16 is positioned between fuel tube 13 and oxygen tube 15. The ends of spiral wire 16 are tack welded to the outer diameter of fuel tube 13. Spiral wire 16 has a diameter of about 0.58mm (0.023 inches). Spiral wire 16 makes four turns around fuel tube 13 and has a pitch of about 4.76mm (3/16 inches). As shown in Fig. 2, the fuel orifice 17 is preferably flush with the fuel orifice 18. However, the fuel orifice 17 may be in front of the oxygen orifice 18, as shown in Fig. 5. Conversely, the fuel orifice 17 may be behind the oxygen orifice 18, as shown in Fig. 4. The most preferred embodiment of the turbulence means is shown in Fig. 1. Within the fuel tube 1 lies turbulence means 2. The turbulence means 2 comprises a flat piece of refractory metal which is welded to the inside of the fuel tube and which is rotated about 90° at its end so that the fuel orifice appears cut into quarters when viewed directly. Between fuel tube 1 and oxygen tube 3 are two spiral wires 5 and 6. The spiral wires 5 and 6 begin as straight wires which are welded at opposite outer sides of the fuel tube at 4a and 4b, about 19mm (0.75 inches) from the fuel orifice. The spiral wires 5 and 6 are again welded to opposite outer sides of the fuel tube at 7a and 7b, about 6.35mm (0.25 inches) from the fuel orifice. From points 7a and 7b the spiral wires 5 and 6 rotate around the outside of the fuel tube till reaching points 8a and 8b, where the spiral wires 5 and 6 are again welded to the outside of the fuel tube. The method of the present invention can use an oxy/fuel burner which deviates in many ways from what is described above, without deviating from the method defined by the claims. For example, the annular oxygen orifice of the burner may be divided into an arrangement of small circular orifices surrounding the fuel orifice. As illustrated in Fig.6, oxygen orifice 40 surrounds fuel orifice 41. Oxygen orifice 40 comprises multiple smaller circular orifices 42 which are arranged in a circle around fuel orifice 41. The oxy/fuel burner illustrated in Fig. 2 was fired for testing. Table 1 shows the results of one firing test. Methane was supplied as fuel. The first column of Table 1 shows the time at which the readings were taken. The fuel flow of the burner, shown in the second and third columns, began at about 340 l/hr (12 SCFH) and was reduced to 227 l/hr (8 SCFH) and finally 57 l/hr (2 SCFH). The oxygen flow, shown in the fourth and fifth columns, began at 748 l/hr (26.4 SCFH) and was reduced to 498 l/hr (17.6 SCFH) and gradually to 42 l/hr (1.5 SCFH). The sixth through tenth columns show the measured temperature in degrees celsius at 50.8, 101.6, 152.4, 203.2 and 254 mm (2, 4, 6, 8 and 10 inches), from the fuel orifice. The Table shows that the highest temperature was measured at 101.6mm (four inches) from the fuel orifice (base of the flame). This remained constant no matter what the fuel flow was. Tables 2, 3 and 4 show data from similar tests using the burner described above. These Tables also show the highest temperature measured at 101.6mm (four inches from the fuel orifice (the base of the flame). Table 4 shows a span of almost seven hours to the first reading of that test to the last reading of that test. TIME GAS OXYGEN DISTANCE FROM FUEL ORIFICE CFH IN.WC. CFH IN.WC 2" (50.8mm) 4" (101.6mm) 6" (152.4mm) 8" (203.2mm) 10" (254mm) 11:30 12.0 7.4 26.4 8.9 777 841 802 774 764 13:16 12.0 7.4 26.4 9.8 916 978 953 936 935 13:26 8.0 3.6 17.6 6.1 --- --- --- --- --- 15:25 8.0 3.6 17.6 6.1 906 956 931 906 884 15:30 2.0 0.5 4.5 1.7 --- --- --- --- --- 16:33 2.0 0.5 4.5 1.5 762 774 752 735 714 16:52 2.0 0.5 4.5 1.5 737 747 723 706 685 TIME GAS OXYGEN DISTANCE FROM FUEL ORIFICE CFH IN.WC. CFH IN.WC 2" (50.8mm) 4" (101.6mm) 6" (152.4mm) 8" (203.2mm) 10" (254mm) ---- 15.0 --- 33.15 23.0 --- --- --- --- --- 13:05 8.3 1.1 22.6 14.2 756 790 739 688 646 14:45 3.5 1.0 8.5 4.8 715 743 715 686 653 14:15 3.3 1.0 8.3 4.7 695 725 695 665 633 TIME FLOW CFH DISTANCE FROM FUEL ORIFICE 2" (50.8mm) 4" (101.6mm) 6" (152.4mm) 8" (203.2mm) 10" (254mm) 10:29 8.0 830 860 849 835 820 10:45 8.0 842 882 870 854 841 11:00 8.0 845 888 877 861 850 11:15 8.0 853 896 881 866 855 11:30 8.0 860 902 886 871 859 11:45 8.0 864 907 890 875 863 12:00 8.0 869 911 894 879 867 12:15 8.0 873 915 898 883 872 12:30 8.0 878 917 903 888 876 12:45 8.0 880 922 906 891 879 TIME GAS OXYGEN DISTANCE FROM FUEL ORIFICE CFH IN.WC. CFH IN.WC 2" (50.8mm) 4" (101.6mm) 6" (152.4mm) 8" (203.2mm) 10" (254mm) 10:10 12 7.5 26.5 9.5 842 896 833 796 785 10:20 12 7.6 26.4 9.5 854 906 844 807 797 10:30 12 7.5 26.5 9.7 874 925 864 828 810 10:35 REDUCED FLOW 10:40 8.0 3.7 17.0 5.8 --- --- --- --- --- 10:50 8.0 3.7 17.0 5.8 857 900 854 826 808 11:00 8.0 3.7 17.0 5.8 850 893 853 823 805 11:10 8.0 3.7 17.0 5.8 847 891 854 823 804 5:00pm 8.0 3.7 17.0 6.4 966 1003 958 923 895 It will be within the reach of an average expect to adapt the foregoing to other thermoplastic materials. In the above tables gas and oxygen flows have been expressed in CFH (cubic feet per hour). To convert to l/hr these figures should be multiplied by 28.3168. Gas and oxygen pressures have been expressed in IN.WC (inches of water). To convert to Pa these figures should be multiplied by 249.089.

Claims: A method of producing glass articles, wherein molten glass flows from a furnace, through a distribution channel, and then to forming means, said method includes forming by means of any oxy/fuel burner, at least one oxy/fuel flame (33) directed from the sides of said distribution channel towards the center thereof, said flame having a hottest point within 127mm (five inches) of the face or outermost part of said burner so as to produce a large thermal gradient between the sides of said distribution channel and the center of said distribution channel. The method of claim 1, wherein said at least one oxy/fuel flame (33) has a hottest point within 76mm (three inches) of the said face or outermost part of the burner. The method of claim 1 or 2, wherein said burner provides between 14 l/hr (0.5 SCFH) and 425 l/hr (15 SCFH) of fuel. The method of claim 3, wherein said burner provides between 198 l/hr (7 SCFH) and 425 l/hr (15 SCFH) of fuel. The method of any preceding claim, including cooling the center of said distribution channel with a longitudinal flow of air. The method of any preceding claim, including separating the sides of said distribution channel from the center of said distribution channel by placing wings (27) in the crown of said distribution channel, said wings projecting downward towards the surface of said glass flowing through said distribution channel. The method of any preceding claim, wherein a stream of fuel is projected from a fuel orifice at a velocity below 152m/sec (500 ft/sec). The method of claim 7, wherein said velocity is below 76m/sec (250ft/sec). The method of claim 7 or 8, including projecting said streams of fuel and oxygen at a oxygen velocity to gas velocity ratio of about 1.5:1.

Inventors: BROWN JOHN THOMAS, TINZ JERRY, BROWN, JOHN THOMAS, TINZ, JERRY, BROWN, JOHN THOMAS, CORNING INCORPORATED, TINZ, JERRY, CORNING INCORPORATED
Applicants: CORNING INC, CORNING INCORPORATED
Application year: 1994
Main classification: C03B7
IPC codes: C03B5, C03B7, F23D14